Having long been at the forefront of space development, astronaut Takao Doi became the first Japanese astronaut to perform an extravehicular activity (EVA) in 1997. From his two flights into space, Doi witnessed firsthand the potential of human space development and the beauty of Earth. His experiences profoundly moved him, and as his perspective broadened over time, he began exploring the relationship between space and life.
Currently, he is a visiting professor at Ryukoku University where he promotes the LignoStella Project, which utilizes wood in the inorganic environment of outer space.
Knowing Doi’s experience with the extreme environment of outer space, Daikin designer Ren Shirayanagi spoke with him about his thoughts on “spaces for people to live.”
Interest Starts with a Boy Gazing at the Stars
Shirayanagi: Thank you for speaking with me today. To be honest, when I was a young boy, I dreamed of becoming an astronaut, so I’m extremely pleased to meet you.
Doi: The pleasure is all mine. My interest in outer space began with my gazing at the stars in my second year of junior high school. From that time onward, I became fascinated with space and continued observing the stars throughout high school. My journal at the time has me writing, “I’ve decided to devote all my energy towards space.” It was that experience that persuaded me to pursue a career in space. After entering university, I majored in astronautical engineering because I wanted to build my own rockets.
Shirayanagi: It must have felt quite exciting for you to fulfill your childhood dream. How did you feel and what memories do you have from your first journey into space as an astronaut?
Doi: What I remember the most is looking out of the space shuttle window and seeing Earth for the first time. Because it was daytime, Earth seemed to have a shining blue appearance, and the color of the ocean and white clouds stood out against the pitch-black background of the universe. Between the earth and outer space rests a thin, blue layer of atmosphere emitting blue light. I remember being deeply moved by it and thinking, “Earth is an amazingly beautiful planet.”
Shirayanagi: This may be a rather basic question, but did you ever feel afraid in space? When you perform an extravehicular activity, there is no air around you, so if you drift away, there is a chance that you may never come back. That must have made you think and caused stress.
Doi: My first flight was on the Space Shuttle Columbia. For the first eight minutes and thirty seconds before we reached orbit, the space shuttle rocket was moving and causing my body to be pressed back against the seat, but I never felt any fear at that time. The flight deck crew was busy piloting, and those of us in the mid-deck where I was sitting were having fun together, so I honestly wasn’t afraid at all.
However, my first EVA was extremely long and lasted about seven hours and forty-five minutes. Once I came back, I realized a bit later, “I was actually out in the infinite expanse of space,” and my body started to tremble. When you're working outside the vehicle, you're excited with the adrenaline pumping and working hard, but once you get back and you start to calm down and feel relieved, a certain type of anxiety creeps in.
Living Environment in Outer Space and Wooden Satellites
Shirayanagi: We often see news reports these days about people and companies making plans to go to the moon or Mars, meaning they’re trying to design a way for people who have never been to space to live there. Since you have been to space, what type of living environment do you think would be best for life on the moon or Mars?
Doi: To begin with, there is quite a difference between living in outer space (zero gravity) and living on the moon or Mars. The moon has one-sixth of Earth's gravity, and Mars has just under one-third. I think that life on a planet with a little gravity, like the moon or Mars, would be easier on the human body. You could also distinguish between up and down. If I were to spend a long time in space, I would prefer living on the moon or on Mars.
Shirayanagi: I suppose that air and temperatures are different in space. What are your thoughts on that?
Doi: Inside the space shuttle, there is a pressure of one atmosphere, and air composition is adjusted to about 80% nitrogen and 20% oxygen, which closely resembles conditions on Earth. The temperature also felt comfortable, so I assume that it is regulated.
Another consideration is design [of the living quarters]. We all probably imagine a life inside a cylindrical aluminum base, but having to live many years in a metal base would seem pretty boring to me. Nor would it seem very interesting to dig a hole and live underground.
That’s why I thought of using wood. When I first began living in Kyoto, I visited many shrines and temples. Most of them were wooden structures, and some of them had been built over 1,000 years ago. That experience made me think that wooden buildings could last 10,000 years in space where there would be no wood damage from rain, insects, or bacteria. Wood is also a material that humans can create, and by working with wood, humans could continue to develop in space for all of eternity.
A search of the literature found that no substantial research had been done into the use of wood in space. To verify that wood could be used, we started the LignoStella Project, which initially involves research and development of a wooden satellite.
Shirayanagi: That's interesting. I had never thought of wood for a satellite. But isn't it true that wood is weak in terms of strength, and that it breathes, making it unsuitable for an oxygen-free space?
Doi: The idea that wood is weak is a myth. Wood contains a polymer crystal called “cellulose,” which is produced by plants, and it has a tensile strength in the direction of its fibers that is as strong as iron. However, the adhesive that holds the cellulose crystals together is weak, so strength in the lateral direction is weak. That’s probably why people think that “wood is weak,” but if used properly, wooden houses can function quite effectively in outer space.
Shirayanagi: I would love living in outer space if the comfort of wooden spaces could be recreated.
Doi: I completely agree. So, to verify that wood can be used in space, we first had to build a wooden satellite. This is the engineering model of LignoSat (showing the model to Shirayanagi), the first wooden artificial satellite from the LignoStella Project. It was used for terrestrial experiments. Structurally, it is exactly the same as the flight model. The material for the six wooden panels comes from honoki, a Japanese magnolia tree. Magnolia trees do not form forests and grow only in isolated areas, so they cannot be harvested in large quantities. However, in Japan, magnolia trees have long been used to make sheaths for Japanese swords since they will not warp from humidity. That’s a useful quality since it would be a disaster if the sheath were to become deformed and prevent the sword from being drawn.
Another feature is its low specific gravity and light weight. We conducted vacuum experiments and confirmed that magnolia is extremely strong in a vacuum with no deformity. An empress tree (Paulownia tomentosa) would have also been good, but it’s too soft and easily damaged, so we decided on magnolia.
Shirayanagi: It’s quite different from our image of satellites. I guess that all it needs are solar panels on its surfaces.
Doi: That’s right. This 10 cm CubeSat was released into space from the International Space Station in December 2024 and remained there for four months until April 2025. The LignoStella Project envisions creating forests on the moon, Mars, and other planets, and then harvesting those trees for humans to build wooden homes, infrastructure, and even space stations. Building a wooden satellite to prove that wood is useful in space was the first step in doing that.
Air Design Inspired by Outer Space
Shirayanagi: Daikin is a company dedicated to “designing the air.” For someone like you, a person who has been to space, what does the concept of “air” mean to you?
Doi: If we go to the moon or Mars in the future, we’ll have to create everything, including air. We would also have to regulate temperature and humidity. For that reason, it’s a situation in which air conditioners literally become essential for the places inhabited by people. That means that the air conditioners had better not malfunction. So, how can we operate them for 10 or 20 years without them breaking down? And if they do break down, they’ll need to either repair themselves automatically or be easily repaired since it would require a tremendous effort to bring them all the way back to Earth for repairs each time.
And when talking about air conditioning, the concentration of carbon dioxide can greatly affect the way people feel. On Earth, it’s around 400 ppm, but when it goes higher, people start to feel irritable. For this reason, I think a system that can regulate the amount of carbon dioxide would be best. Incidentally, when I wanted to calm myself, I would often look out the window at Earth. To me, that was the ultimate method to relaxing. The ability to relax in space is a very important aspect, so if air could be used to create relaxing spaces, then the possibility of humans living in space would become more likely.
Shirayanagi: In outer space, it is certainly true that air not only provides comfort but also supports life. That makes it important to design air that accounts for such factors as temperature, humidity, and air quality along with air that considers people’s feelings and provides them with a sense of security.
Speaking with you today has reaffirmed the value of our work in “designing the air” from the standpoint of creating environments where people can be themselves, both here on Earth and in space. Thank you for sharing your valuable perspective with us today.
